1. Field of the Invention
The invention relates to a flat tube for a heat exchanger which has long beads formed to form a plurality of passages within the tube, and particularly enables to securely determine a tube insertion level.
The invention relates to a flat tube for a heat exchanger which has long beads formed to form a plurality of passages within the tube and pressure resistance enhanced, and particularly the improvement of compressive strength in the neighborhood of joined sections between the flat tubes and the header tanks.
2. Description of the Related Art
Generally, a conventionally known laminated heat exchanger has a plurality of flat tubes laminated in parallel to one another, both ends of the respective flat tubes connected to two header pipes, and inlet and outlet joints disposed at predetermined points of the header pipes to receive and feed a heat-exchanging medium. And, in this heat exchanger, the fed heat-exchanging medium is meandered a plurality of times to flow between the header pipes through the flat tubes while heat-exchanging with outside. The flat tube used in such a laminated heat exchanger, as shown in FIG. 11 in a transverse cross sectional view, is formed by brazing two plates 21, 21 which are formed of brazing sheets formed to have a predetermined size into a flat tube 20. And, a plurality of beads 22, 22 which are protruded to a height so as to contact the end surfaces with the inner surface of the other plate are formed at predetermined points of these plates 21, 21 along its longitudinal direction to form a plurality of passages 24, 24 for the medium within the tube, thereby enhancing a heat-exchanging efficiency and improving pressure resistance of the tube itself. And, both ends of the tube are formed to have flat sections without any beads so as to be inserted into the insertion holes of the header pipes, so that airtightness between the tubes and the header pipes is secured.
Reference numerals 23, 23 denote flat joined sections disposed at both ends of the plates 21, 21, and joined areas are expanded by these joined sections 23, 23, so that satisfactory brazing strength can be secured. And, in addition to this two-split structure, a flat tube is known to be formed by bending a single plate and mutually bonding the ends in the breadth direction of the plate.
Besides, the heat exchanger provided with such flat tubes is precision equipment and needed to have pressure resistance to meet respective applications. For example, the heat exchanger to be used as a condenser is required to have high pressure resistance, and adhesion of respective parts by brazing is required to be satisfactory.
Furthermore, in assembling this flat tube to the header pipes, it is significant to control the insertion level of the flat tube into the header pipes. Specifically, if the respective tube insertion levels can not be kept constant, the flow rate of the medium flowing through the respective tubes may be deviated, or the smooth flow of the medium between the tubes and the header pipes may be adversely affected, thus it is directly related to the heat-exchanging performance, and the pressure resistance of tubes may be deteriorated.
For example, in a tube group consisting of a plurality of tubes, since the medium flows relatively smoothly at the tube ends which are inserted in a small extent into the header pipes, it flows in a large amount into them, but at the tube ends which are inserted in a large extent into the header pipes, such flow-in is prevented and the medium flows in a small amount. The tubes into which the medium flows in a large amount are insufficient to effect heat exchange, and the tube group as the whole has its heat-exchanging performance degraded.
And, when the tube insertion level is not uniform as described above, the flat sections of the tubes formed in the neighborhood where the tubes are joined with the header pipes have a different length, and as compared with the short flat sections, the long flat sections are easily deformed by the internal pressure due to the medium, and the tubes as the whole are degraded in pressure resistance.
And, as a method to secure the precision of the tube insertion level, various types of stopper members are generally disposed at a predetermined point in the tubes, namely a distance according to the tube insertion level from the tube ends.
It is known to dispose stoppers by, for example, (1) projections which are formed at predetermined points on the flat sections disposed at the tube ends to intersect at right angles in the longitudinal direction of the tube and to protrude in vertical directions by pressing and used as stoppers (e.g., Japanese Patent Laid-Open Publication No. Hei 2-242095), (2) insertion sections which suit the header pipe insertion holes are formed at both ends of the flat tubes, and contact sections which serve as stoppers are formed in the longitudinal direction of the tubes (e.g., Japanese Utility Model Laid-Open Publication No. Hei 2-28986), (3) predetermined sections of tubes in the breadth direction are pressed to be flat to form projections which are protruded outside in the breadth direction of the tubes, and the projections are used as stoppers (e.g., Japanese Utility Model Laid-Open Publications No. Hei 3-21664, No. Hei 7-2780, No. Hei 7-2781), and stopper members which are formed on the side of the header pipe instead of forming on the side of the tubes are also known. Specifically, there is also proposed (4) header pipes have a two-split structure with a tube divided at the center line in the longitudinal direction, and stopper projections which are in contact with the tube ends are integrally formed at predetermined points in the header pipes in which the tubes are inserted (e.g., Japanese Patent Laid-Open Publication No. Hei 6-94384).
And, a laminated heat exchanger provided with such flat tubes is produced by assembling respective parts into a predetermined structure and integrally brazing in a furnace. Specifically, fins are disposed between the respective flat tubes, both ends of the flat tubes are inserted into the tube insertion holes of the header pipes and fixed by a jig, and integrally brazed in the furnace. Therefore, the joined surfaces of the tube insertion holes of the header pipe and the flat tubes and the end faces of the beads in the flat tubes are joined by integrally brazing.
However, the conventional flat tubes for a heat exchanger described above had the following disadvantages.
Specifically, (1) described above needs a separate process for the projections for press forming of the flat sections on the tubes, and since the projections are formed to intersect at right angles in the longitudinal direction of the tube, the passage shape in the tube is disturbed, and the smooth flow of the medium is disturbed in the neighborhood of the inlet and outlet sides of the tubes. Especially, the liquefied medium might be accumulated at the projections on the lower side, degrading the heat-exchanging performance.
And, (2) described above has complex structures at the insertion and contact sections of the tube ends, being disadvantageous because not suitable for producing in a large quantity. And, when the contact sections are formed in the longitudinal direction of the tubes, the contact sections are not easily used for heat-exchanging, degrading the efficiency of the heat exchanger.
Besides, (3) described above forms a part of the tube by pressing and needs to process without deforming the tube itself, requiring high processing precision. Especially, when the tubes to be used for a compact and light-weight type are thin, high processing precision is required to prevent the processed parts from being communicated with the inner passage, or pressure resistance of the processed parts may be degraded.
Furthermore, (4) described above disposes the stopper projections integrally at the predetermined points inside the header pipes, and the header pipes are required to have the two-split structure. Therefore, the structure cannot be made simple, it is disadvantageous to produce in a large quantity, and the production cost cannot be lowered. And, the stopper projections are positioned in the neighborhood of the tube ends where the medium is flown in or out, and the flow of medium within the header pipes and through the tubes may be disturbed by the stopper projections.
Besides, there are proposed such a flat tube in which beads are formed in spots to cause turbulence in the medium flowing the interior, thereby promoting heat exchange by a turbulence effect (e.g., Japanese Patent Laid-Open Publication No. Hei 7-19774), beads are not formed in the neighborhood of the joined sections of the flat tubes and the header tanks to make them flat, thereby securing the joint between the flat tubes and the header tanks (e.g., Japanese Patent Laid-Open Publication No. Hei 6-159986), and joining sections of the header tanks are extended towards the tubes to cover the outsides of the tube ends, thereby securing the joint (e.g., Japanese Patent Laid-Open Publication No. Hei 8-49995).
And, a laminated heat exchanger provided with such flat tubes is produced by assembling respective parts into a predetermined structure and integrally brazing in a furnace. Specifically, fins are disposed between the respective flat tubes, both ends of the flat tubes are inserted into the tube insertion holes of the header tank and fixed by a jig, and integrally brazed in the furnace. Therefore, the joined surfaces of the tube insertion holes of the header tank and the flat tubes and the end faces of the beads in the flat tubes are joined by integrally brazing.
However, the conventional flat tubes for a heat exchanger described above provided with the long beads in a plurality of rows had a disadvantage that pressure resistance is lowered in the neighborhood of the joined sections with the header tanks.
Specifically, as shown in FIG. 12 for example, when distances x, y from end sections 22a of respective long beads of flat, tubes forming flat sections which are disposed instead of beads at both ends of a flat tube 20 to the outer periphery of a header tank 4 to which the flat tube 20 is connected are different to each other, a longer one is disadvantageous in view of pressure resistance, the tube 20 is largely deformed, and the heat-exchanging performance may be failure and the structure may be damaged. And, when the tube 20 is deformed by the pressure of the medium flowing therein and all tubes 20, 20 for the beat exchanger are also deformed, the shape of the heat exchanger as the whole is deformed due to a totaled deformation force, and airtightness of the joined sections between the tubes 20 and the header tanks 4 may not be retained. Therefore, since the flat tubes cannot keep sufficient pressure resistance, a core is deformed and performance is degraded. For example, a condenser has specifications disadvantageous in view of satisfying pressure resistance.
The flat sections of the tube 20 are desired to be close to the tube insertion hole of the header tank 4 and small as much as possible, but it is hard to make it uniform due to deviations in assembling the heat exchangers. And, a step for especially uniformizing may be disposed, but it increases the production cost because the number of process steps is increased.
Therefore, as shown in FIG. 13 the bead end sections 22a are formed into a shape to intersect at right angles in the longitudinal direction of the tube, the header tank 4 is formed of two members 4A, 4B, the header tank 4B opposed to the tubes 22 is formed to have a transverse cross section in the same shape to intersect at right angles, and the flat section of the tube 20 may be removed. But, the header tank 4 has its shape limited and its design is also limited, and productivity of the tank and performance of the heat exchanger may be interfered. Besides, when the header tank 4B is formed to have a transverse cross section in the above-described shape of intersecting at right angles, pressure resistance is insufficient.